Loudspeaker



Patented Nov. 29, 1938 UNITED STATES LOUDSPEAKER Gabriel E. Sundstrom,

Sundstrom Pressed S corporation of Illinois Application October 17,

1 Claim.

This invention relates to loud speakers of the general type now more or less commonly used in connection with radio receiving apparatus and for other sound amplification purposes.

. The main objects of the invention are to provide a loud speaker construction having a greater electrical and magnetic eificiency; to provide a structure of high efficiency butof simplified construction; to provide an improved construclo tion for certain parts of such a loud speaker; and

in general, it is the object of the invention to provide an improved loud speaker construction of the type referred to. s

This application is continuation in part of my id copending application Serial No. 61,883, filed February 1, 1936.

In the drawing:

Fig. 1 is a vertical speaker embodying the Fig. 2 is a front view ture shown in Fig. 1;

Figs. 3, 4, and 6 illustrate successive steps in the production of the form of field member illustrated in Figs. 1 and 2; v

Fig. 7 is a plan of a blank embodying another arrangement for joining its ends to form the field member; and

Fig. 8 is a perspective of the field member formed from the blank shown in Fig. 7.

Referring now to the drawing, the loud speaker construction illustrated in Fig. 1 embodies a main element'or magnetic field member designated l0 which, in this instance, is Iormed of a flexible soft metal memberbent to closed loop 5 form as illustrated. The member I0 is illustrated separately in Fig. 6 from which it will be seen that it is formed from an elongated blank or strap of sheet metal bent to the form indicated. Front and back walls Ii and I2, respectively, of the field member In are provided with openings l3 and I4, respectively. The top and bottom or opposite end walls I5 and I6 respectively, of the field member, are in this instance illustrated as being somewhat shorter than the front and back walls Hand i2, the relative lengths of the walls being, of course, suited to the size of magnetic coil, such as H, to be positioned within the field member. or to other requirements of the speaker to be made.

A pole piece I8 of suitable magnetic metal and usuallv of cylindrical shape, is assembled with the field member by first positioning the coil II within the field member and then inserting the pole piece'through the opening I3 in the front wall of the field member, through the coil I! and cross section or a loud present invention; of a portion of the struc- Chicago, Ill., assignor to teel 00., Chicago, 111., a

1936, Serial No. 106,093

then into the opening I 4 in the rear wall of the field member. The openings I3 and M are preferably simultaneously machined to finished sizes by suitable means such as a reamer which may embody an end portion which will provide the opening I of a predetermined diameter, and another portion which will ream the opening i 3 to predetermined size co-axially aligned with the opening l4. Reamers embodying the necessary two parts for simultaneously reaming the said opening are well known tools and therefore no illustrated.

As already indicated when the pole piece i8 is inserted, a magnetic coil I1 is also assembled in place. The coil Ii is normally wound on a suitable sleeve element through which the pole piece I8 may be passed. The fit oi the pole piece l8 in the sleeve of the coil I1 is preferably a fairly snug but slidable fit. The pole piece is inserted, rear end first, through the voice coil opening l3 until the rear end reaches the opening [4. The opening I4 is made of such size that the rear end of the pole piece must be 'forceably driven into said opening, which, when done, results in a rigidly and practically permanently mounted and positioned pole piece. If

required, a suitable ring or other gauge device may be employed for insuring accurate centering of the front end of the pole piece in the voice coil opening l3 which is of course large enough to receive a voice coil l9 carried by a cylindrical apex extension 20 of a cone or tympanum 2|. The tympanum 2| may be mounted in and carried by a so-called basket 22, preferably of stamped sheet metal construction, the same being attached to the field member ill by any suitable means, for example, through the agency of ears and welding as explained in my said copending application.

A transformer 23, from which varying electrical currents pass to the voice coil l9, may be attached to the speaker through the agency of a suitable bracket 24 secured to the field member [0 by welding or otherwise.

The sheet metal blank from which the field member ID is made (illustrated in Fig. 3), embodies the back wall portion I 2 provided with the punched in opening I 4, end wall portions i5. I 6, and end sections Ila and Nb respectively, which together constitute the front wall H of the field member. As indicated, the end portion Ila is provided with a semi-circular recess |3a disposed centrally of the end of the blank, and a pair of dovetail shaped recesses 25, 25. The opposite end 01' the blank is also provided with shaped tongues 26, 2' respectively,

' openings sofas-to obtain a semi-circular recess lib disposed centrally of the width of the blank and a pair of dovetail disposed on opposite sides of the recess lib. The Ba and 25, 25 are respectively complementary to the recess lib and tongues 20, 2!.

The second step in forming a field member from the blank illustrated in Fig. 3 is to bend down the end portion Ila to substantially right angles to the main body portion of the blank and the end portion D to an angle somewhat less than 9!! degrees, substantially as illustrated in Fig. 4. A third step is illustrated in Fig. 5, where the end portions l5 and it are bent to right angular relation to the central or back portion l2. A final step consists in further bending the end portion Nb of the blank into co-planar relation with the end portion Ha, in which position the dovetail shaped tongues, 26, 26 will enter and lock with the dovetail shaped recesses 25, 25. The dovetail tongues and slots are madeo! such relative proportions that when they are interengaged, as shown in Figs. 2 and 6, the meeting ends are more or less jammed into one another so that there is tight, intimate engagement between the ends of the wall portions [la and llb. By reason of the tight fitting interlocked connection resulting from the described arrangement, other'securement or connection between the blank ends, for example, welding, is not required.

The'hole I4 may be employed for guiding purposesduring any of the forming operations where such use is feasible, and it will of course be evident that the procedure may'be-inverted, i. e., the blank ends bent upwardly instead of downwardly, to meet practical considerations in press maintenance and operation.

Suitable punch-press squaring operations may be employed for insuring the desired squareness of the field member. e

Because of the increased area of contact between the'meeting ends ofthe blanks, incident to the described end connections, certain desirable electrical effects are obtained. It also will be apparent that by effectively interlocking the meeting ends of the blanks as described, the practicability. of forming the field member from a blank with prepunched pole piece and voice coil openings in the front and backof the field member is enhanced. The previously described reaming operation is capable of finishing the the required, accurate,

coaxial alignment of the holes.-

The arrangement shown in Figs. 3 to 6 incl 1b slve, has certain. electrical or magnetic advanthe bottom-wall blank shown otherwise as may be at least theoretically. However, a very satisfactory construction, which, for is'preferable, is shown in Figs. arrangement therein. shown, the blank is provided with two punched openings l3 and I4 in portions of the blank which will ultimately form the front and rear walls of the field member. As indicated in Fig. (,the blank comprises a top wall portion to, front and rear wall portions II and I2 respectively, and end portions lfia and 1817 which cooperatively form l6 of the field member.

The end portions I and Nb are respectively provided with a'dovetail shaped recess 21 and a complementary tongue 28, the said recess and tongue being aligned, preferably centrally of the width of the blank. By bending operations similar to those illustrated inFlgs. 3 to 6 inclusive, the in Fig. '7 may be bent to form the elosedloop field member illustrated in Fig. ii wherein the dovetail joint between the ends of the blank are located in the bottom wall It of the field member. Squaring and reaming operations as previously mentioned may be performed on the field member shown in Fig. 8 and a suitable pole piece may be mounted by press fitting or preferred.

The described magnetic field structures are especially advantageous first, in that the required, manufacturing operations are very simple and lnexpensive to-perform, and secondly, in that they provide an emcient magnetic fiux circuit, thereby adding to the efiiciency of the loud speaker.

tages. efilcient and practical purposes 7 'and 8. In the The emciency of the magnetic fiux circuit is due in considerable measure to the adequate connec-' tion between the meeting ends of the blank when formed into the closed loop illustrated.

Changes in the construction may be made without, departing from the spirit of the invention, the scope of which should be determined by reference to the following being construed as broadly as possible consistent with the state of the art.

I claim:

A magnetic field member for a loud speaker, comprising an elongated flexible soft metal strap bent to form a closed loop, a portion of said loop being provided with a, voice coil opening, said claim, the same strap having meeting end portions provided with asman s. snuns'mou. 

